1. Field of the Invention
The present invention relates to a step counter and a method of counting steps that count steps based on an acceleration generated due to vibrations at the time of walking, and, more particularly, to a step counter and a method of counting steps that realize accurate step counting by accurately discriminating walking from non-walking in a simple manner.
2. Description of the Related Art
In Japan, step counters which count steps are generally called “Manpo-kei”, which is a registered trademark owned by Yamasa Tokei Keiki Co., Ltd. in Japan. Some step counters are provided with an acceleration sensor as described in Japanese Patent Application Laid-Open No. H9-223214. The step counter of this type is attached to a waist of a user, for example, and counts the number of steps according to changes in an acceleration generated due to walking. During steady walk of the user, the acceleration changes periodically. Therefore, the step counter can find the number of steps based on the number of peaks of sensor values of the acceleration sensor.
In one-step walking, a peak of a mountain and a bottom of a trough are included (hereinbelow “peak” may mean both the peak of a mountain and the bottom of a trough). Some step counters do not count a step when the difference between the peak of a mountain and the bottom of a trough (hereinafter also referred to as peak-to-peak difference) is below a predetermined threshold regarding that the corresponding acceleration change is caused by vibrations other than walking. Such a step counter does not count a relatively small vibration as a step. For example, a vibration caused by a toe touching the ground after a heel touches the ground is not counted as a step. Thus, accuracy of the results of counting can be enhanced.
Furthermore, Japanese Patent No. 3685741 describes a step counter in which plural thresholds are set to be compared with the peak-to-peak difference for the discrimination of walking from non-walking. This step counter changes a set threshold to a larger one after detecting a vibration with a large peak-to-peak difference, and to a smaller one after detecting a vibration with a small peak-to-peak difference.
The step counter described earlier, however, has some limitations in accuracy enhancement, since it counts the steps based only on the peak-to-peak difference of the sensor values detected by the acceleration sensor. Depending on a walking speed, the same peak-to-peak difference can indicate both the walking and the non-walking. Therefore, the determination based only on the comparison between the peak-to-peak difference and the threshold cannot always realize accurate step counting. In addition, if the step counter falls off and vibrates instantaneously, a peak may appear in the sensor values of the acceleration sensor. Then, the step counter may erroneously count one step according to this peak.
On the other hand, the step counter of Japanese Patent No. 3685741 changes the threshold according to the size of peak-to-peak difference. Therefore, the step counter can adjust itself to some extent to the fluctuation in a boundary between the walking and the non-walking according to the walking speed. However, for the accurate step counting, it is necessary to previously set an optimal combination of thresholds from a large number of combinations. In addition, when an instantaneous vibration not attributable to the walking exhibits a large peak-to-peak difference, it is still counted as a step.